ROME, Italy (CNN) -- Countries and donors must spend as much as $20 billion a year if the world is to end the food crisis, the head of the United Nations said Wednesday.

A woman protests in Dakar, Senegal, against the recent price rise for basic food-stuffs.

Ban Ki-moon spoke to reporters on the second day of a U.N.-organized summit in Rome to deal with food security -- a broad term that includes hunger, rising food prices, food production, high oil prices, and climate change.

"Addressing the world food crisis in all its immediate and longer-term aspects requires substantial and sustained financial and political commitment," he said.

Ban cited progress at the summit so far, with delegates showing resolve, responsibility and political commitment to solving the problems, but he urged them not to leave the summit without implementing a clear plan of action.

"We must not address only the immediate symptoms of the problem -- that of soaring food prices," he said. "We must focus on the underlying causes of the problem: years of neglect of the agricultural sector around the world, and the lack of investment in increasing productivity."

He called on nations to take four immediate steps:

Make the international trade system work more effectively so more food is available, and at reasonable prices;

Increase humanitarian aid to cushion the impact of high food prices on vulnerable populations;

Find a way to boost harvests in the next year and continue investment in agriculture over the long run;

Help governments struggling to cope with the food crisis through fiscal support.

"Substantial new resources will be needed -- perhaps as much as $15 to $20 billion a year as our efforts build up," Ban said.

The World Food Program said Wednesday it has given an extra $1.2 billion in aid to 62 countries hardest hit by the global food crisis. The U.N. agency is already providing some $5 billion to 90 million people in 78 countries this year.

Countries that will receive the extra injection of aid include Haiti, where riots have broken out in recent months over high food prices. The WFP said it is "fast-tracking" the aid to Haiti and tripling the number of Haitians who can receive food.

In Afghanistan, the extra money will allow food aid to reach an additional 2.5 million people, almost half of whom are urban residents priced out of the wheat market, the WFP said.

The agency is sending $163 million of the extra funds to Somalia, where high food prices are compounding the existing problems of drought, hyper-inflation and continued conflict, the WFP said. Some $193 million will go toward urgent food distribution in Ethiopia, which is suffering from high prices and drought, the WFP said.

Ban praised French President Nicolas Sarkozy for pledging more than $1.5 billion over the next five years to boost agricultural productivity in Africa.

Saudi Arabia has already announced it is giving around $500 million to the World Food Program to deal with the emergency in the short term, and the United States has committed some $5 billion over the next two years, much of it to help find long-term solutions.

"This is a fight we cannot afford to lose," Ban said. "The enemy is hunger."

Ban opened the three-day summit Tuesday, but it quickly degenerated into recriminations with the presidents of Iran and Zimbabwe blaming the West for the millions starving around the world.

Zimbabwean President Robert Mugabe said Britain is to blame for the food crisis in his country. He said Britain persuaded its allies in Europe, North America and elsewhere to impose "illegal" economic sanctions on his country and to cut off developmental assistance.

Critics say Mugabe's own policies are to blame for the dramatic drop in food production and agricultural exports in Zimbabwe, a country once known as southern Africa's "breadbasket."

On Wednesday, a U.N. official in Zimbabwe told CNN the government had ordered at least 30 aid agencies to stop their work. The agencies provide food, health care and other services to some of the poorest and most vulnerable people in the Zimbabwe.

The world's population is expected to grow to 7.2 billion by 2016, up from today's 5.7 billion, according to the United Nations. The United Nations says that 862 million people around the world are hungry.

The United Nations says high oil prices, climate change, competition between biofuel and food production, and speculation on agricultural commodities in world markets are all contributing to the food crisis.